Erectile dysfunction (ED) is a serious medical condition that affects 52% of men between the ages of 40 and 70 and costs in excess of $150 million for inpatient care alone (1985 dollars). Diabetes is a contributing factor in 50% of individuals with ED. Current treatment options for ED are only partially effective (Vale, 2000). Therefore a need exists to develop new therapeutic approaches to treat ED. The process of erection involves critical integration of vascular, neural, hormonal and morphologic* influences. As ED develops the balance between these processes becomes skewed. In both diabetic and cavernous nerve injury induced ED models, profound alterations in smooth muscle and endothelial function and abundance commonly accompany the observed impotence. Current treatments for ED aim to increase the available NO and thus smooth muscle relaxation. However as the smooth muscle morphology of the corpora cavernosa becomes increasingly abnormal, these traditional treatment strategies become less effective and eventually fail. In this application we propose a novel approach, in which we aim to elucidate the underlying mechanisms that cause corpora cavernosa smooth muscle abnormalities and thus ED to occur. Sonic hedgehog (Shh) is a crucial regulator of penile morphology. Shh inhibition alters per morphology such that smooth muscle and endothelium significantly decrease, the sinusoid architecture collapses and ED occurs. The morphological and physiological changes of the Shh inhibited penis parallel observations of smooth muscle loss and decreased Shh protein in diabetic and CN injured rat models of ED and in human diabetic penes, thus implicating a physiological link between decreased Shh protein and ED. Shh protein treatment can induce VEGF and NOS, thus suggesting a potentialmechanism through which decreased Shh protein can cause ED. We propose the hypothesis that Shh inhibition represents an underlying cause of ED rather than a symptom of smooth muscle loss. Increasing our understanding of Shh signaling in the penis will provide valuable insight that may lead to new treatment strategies for impotence.